Dual discharge modes operation for remote plasma

ABSTRACT

Embodiments of the present technology may include a method of processing a semiconductor substrate. The method may include providing the semiconductor substrate in a processing region. Additionally, the method may include flowing gas through a cavity defined by a powered electrode. The method may further include applying a negative voltage to the powered electrode. Also, the method may include striking a hollow cathode discharge in the cavity to form hollow cathode discharge effluents from the gas. The hollow cathode discharge effluents may then be flowed to the processing region through a plurality of apertures defined by electrically grounded electrode. The method may then include reacting the hollow cathode discharge effluents with the semiconductor substrate in the processing region.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. ProvisionalApplication No. 61/872,064 filed Aug. 30, 2013 and titled “DUALDISCHARGE MODES OPERATION FOR REMOTE PLASMA REMOVAL PROCESS OFSICONI/CHISEL”, the entire contents of which are hereby incorporatedherein by reference for all purposes.

FIELD

The present technology relates to semiconductor systems, processes, andequipment. More specifically, the present technology relates to systemsand methods for reducing film contamination and improving deviceperformance.

BACKGROUND

Integrated circuits are made possible by processes which produceintricately patterned material layers on substrate surfaces. Producingpatterned material on a substrate requires controlled methods forremoval of exposed material. Chemical etching is used for a variety ofpurposes including transferring a pattern in photoresist into underlyinglayers, thinning layers, or thinning lateral dimensions of featuresalready present on the surface. Often it is desirable to have an etchprocess that etches one material faster than another facilitating, forexample, a pattern transfer process. Such an etch process is said to beselective to the first material. As a result of the diversity ofmaterials, circuits, and processes, etch processes have been developedwith a selectivity towards a variety of materials.

Etch processes may be termed wet or dry based on the materials used inthe process. A wet HF etch preferentially removes silicon oxide overother dielectrics and materials. However, wet processes may havedifficulty penetrating some constrained trenches and also may sometimesdeform the remaining material. Dry etches produced in local plasmasformed within the substrate processing region can penetrate moreconstrained trenches and exhibit less deformation of delicate remainingstructures. However, local plasmas may damage the substrate through theproduction of electric arcs as they discharge or if a high enoughselectivity is not achievable.

Thus, there is a need for improved systems and methods that can be usedto produce high quality devices and structures. These and other needsare addressed by the present technology.

SUMMARY

A hollow cathode discharge may be a plasma discharge that increases theelectron impact ionization rate at the center of a hollow cathode, aso-called virtual anode, by pendulum electrons emitted from a cathodesurface under a particular pressure-diameter of hollow cathode (pD)condition. Generating a hollow cathode discharge for semiconductorprocessing, and possibly alternating generation of the hollow cathodedischarge with generation of a glow discharge in the same processingchamber, may provide advantages in semiconductor processing.

Embodiments of the present technology may include a method of processinga semiconductor substrate. The method may include flowing gas through acavity defined by a powered electrode. The method may further includeapplying a negative voltage to the powered electrode. Also, the methodmay include striking a hollow cathode discharge in the cavity to formhollow cathode discharge effluents from the gas. The hollow cathodedischarge effluents may then be flowed to the processing region througha plurality of apertures defined by electrically grounded electrode. Themethod may then include reacting the hollow cathode discharge effluentswith the semiconductor substrate in the processing region.

Embodiments may include a method of processing a semiconductorsubstrate, where the method may include flowing gas to a processingregion. Additionally, the method may include striking a hollow cathodedischarge to form hollow cathode discharge effluents from the gas.Furthermore, the method may include reacting hollow cathode dischargeeffluents with the semiconductor substrate in the processing region. Themethod may also include striking a glow discharge to form glow dischargeeffluents from the gas. The method may further include reacting glowdischarge effluents with the semiconductor substrate in the processingregion.

Embodiments of the present technology may include a system forprocessing a semiconductor substrate. The system may include a poweredelectrode electrically coupled with an electronic ballast. Additionally,the system may include a conical cavity defined by the poweredelectrode, where the conical cavity is characterized by a narrowerdiameter end and a wider diameter end. The system may further include apower supply electrically coupled with the electronic ballast, where thepower supply is configured to deliver a negative voltage at a frequencybelow about 1 MHz to the powered electrode to strike a hollow cathodedischarge in the conical cavity. The system may also include a gas inletconnected to the narrower diameter end of the conical cavity.Furthermore, the system may include an electrically grounded electrodedefining a plurality of apertures, where the electrically groundedelectrode is disposed closer to the wider diameter end of the conicalcavity than the narrower end of the conical cavity. The electricallygrounded electrode may have a first surface and a second surface, andboth the first surface and the second surface may be substantially flat.

Embodiments of the present technology may provide improvements insemiconductor processing. A hollow cathode discharge may be more stableat higher operating pressures. Higher pressure processing may allow forincreased densities of radicals, ions, and other species. Hollow cathodedischarges may also increase the distance that electrons travel, and theincreased travel distance may increase the probability that an electronwould collide with a neutral atom to ionize the atom and generateanother electron. The increased densities may result in faster etchingof or depositing on a semiconductor substrate. Additionally, possibly asa result of increased densities or different chemistries, processingwith a hollow cathode may allow for a more selective process thanconventional processing.

The ionization processes in a hollow cathode may result in electronsremaining in a cavity space defined by an electrode and may result inless damage to the electrode, increasing process reliability andequipment uptime. The hollow cathode discharge may increase the amountof electron impact ionization (i.e., alpha process) and decrease theamount of ionization from secondary electrons (i.e., gamma process). Theincrease in the amount of electron impact ionization may also decreasedamage of cathode and anode surfaces. Moreover, operating a plasma intwo different discharge modes may permit increased precision, control,and/or flexibility in semiconductor processing. Embodiments of thepresent technology provide these and other advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the disclosedtechnology may be realized by reference to the remaining portions of thespecification and the drawings.

FIG. 1 is a graphic showing a bipolar oscillating voltage, a cavitydefined by a powered electrode, and resulting plasma location accordingto embodiments.

FIG. 2 is a graphic showing a unipolar oscillating voltage and resultingplasma according to embodiments.

FIG. 3 is a flow chart of a substrate processing method according toembodiments.

FIG. 4 is a flow chart of a substrate processing method according toembodiments.

FIG. 5 shows a substrate processing chamber according to embodiments ofthe present technology.

FIG. 6 shows a substrate processing chamber according to embodiments ofthe present technology.

FIG. 7 shows a showerhead of a substrate processing chamber according toembodiments of the present technology.

FIG. 8 shows a substrate processing system according to embodiments ofthe present technology.

FIG. 9 shows the voltage and current waveforms of plasma dischargesaccording to embodiments.

FIG. 10 shows images of plasma discharges at various pressures forpositive and negative applied voltages according to embodiments.

DETAILED DESCRIPTION

Semiconductor patterning may involve patterning an upper layer alongwith an underlying layer. Semiconductor processing technology may alsoremove at least a portion of the upper layer while retaining theunderlying layer. Conventional semiconductor processing technology mayremove at least some of the upper layer but may still affect theunderlying layer. The underlying layer may itself be etched partiallyaway, thereby changing the initially patterned profile. Furthermore, theremoval of the upper layer may also deposit contaminants on theunderlying layer or affect the structural, electrical, or otherproperties of the underlying layer. Conventional processing may involvelower gas pressures and lower ion, radical, and electron densities. Alower concentration of reactive species may increase time needed forpatterning a semiconductor substrate. Furthermore, conventionalprocessing may not confine electrons to a space, and these electrons maycollide with and damage electrodes or other portions of the chamber.Damage of electrodes or the chamber may reduce equipment availabilityand increase costs. Conventional processing may also require additionalprocessing operations or equipment. These conventional methods maydetrimentally degrade the performance of the semiconductor device.Embodiments of the present invention may provide improvements insemiconductor patterning technology.

Reference is now made to FIG. 1, which is a graphic showing a bipolaroscillating voltage used to drive a powered electrode and the plasmalocations which have been found to occur during the positive andnegative swings embodiments. A bipolar sinusoidal voltage is shown andmay be symmetric around electrical ground. The bipolar sinusoidalvoltage may represent a sinusoidally varying voltage (varying in time)applied to an electrode relative to a grounded electrode having aplurality of apertures. The powered electrode may not be planar and thegrounded electrode may be planar according to embodiments. As shown, theplasma has been found to change positions within the remote plasmaregion between the powered electrode and the grounded electrode. Thegrounded electrode may be a perforated plate. The bipolar sinusoidalvoltage may initially swing positive such that the powered electrode maybe positively biased relative to the grounded electrode. During thistime, the plasma may be located close to the grounded electrode. Whenthe sinusoidal voltage swings negative, the powered electrode may benegatively biased relative to the grounded electrode and the plasma mayswitch to a position farther away from the grounded electrode. Othershapes of bipolar oscillating voltages may be used to drive the poweredelectrode and the locations of the two plasma excitations would besimilar.

The non-planar electrode may be referred to as a concave electrode, apowered-electrode, or a hollow cathode when the interior surface iscup-shaped or conical as shown. A concave electrode may form a largervolume near the center of the remote plasma region. A perpendiculardistance from the grounded electrode to a concave electrode may begreater near the center of the grounded electrode than a perpendiculardistance from the perforated plate to the electrode near the edge. Theremote plasma on the left of FIG. 1 may be referred to as “glowdischarge mode” and the remote plasma on the right of FIG. 1 may bereferred to as “hollow cathode mode.” The concave electrode may benegatively biased during the hollow cathode mode, which may direct ionsaway from the grounded electrode and may reduce sputtering effects.Visual inspection of both the concave electrode and the groundedelectrode has shown less damage to the electrodes under hollow cathodedischarge operation than glow discharge operation. The groundedelectrode may be coated with nickel in embodiments. A substrate may bedisposed below the grounded electrode during processing and substrateshave been found to possess more micro-contamination (in the form ofelevated particle count) in glow discharge mode relative to hollowcathode mode. The benefit may also arise from the location of the plasmarelative to the grounded electrode and may result from the presence ofthe nickel coating.

FIG. 2 is a graphic showing a unipolar oscillating voltage according toembodiments. A bipolar sinusoidal voltage may be processed to switch thesign of the positive swing, in embodiments, so that the resultingunipolar oscillating voltage may possess two negative swings per periodof the original bipolar sinusoidal voltage. The period of the unipolaroscillating voltage may be half the period of the original bipolarsinusoidal voltage. The unipolar oscillating voltage may still be arepetitive oscillating voltage but may not be referred to as asinusoidal oscillating voltage anymore. The unipolar oscillating voltagemay be applied to the concave electrode, and the plasma maypredominantly form in the same portion of the remote plasma regionduring every peak of the unipolar oscillating voltage and not just halfof the peaks. The bipolar sinusoidal voltage may be processed by passingthe bipolar sinusoidal voltage through a diode bridge formed from anyappropriate type of four diodes. High voltage bipolar sinusoidalvoltages may be processed using IGBT (insulated gate bipolar transistor)diodes and low voltage bipolar sinusoidal voltages (less than 1-2 kV)may be processed using FET-style diodes. A full bridge rectifyingcircuit may eliminate the ability of the bipolar oscillating voltage toexcite a plasma so only a portion of a rectification operation isperformed on the bipolar sinusoidal voltage as shown in FIG. 2.Alternatively, the bipolar sinusoidal voltage may be processed with amore simplistic circuit (involving e.g. a single diode) to create aunipolar oscillating voltage with one negative swing for each period ofthe original bipolar oscillating voltage. In this case, the unipolaroscillating voltage may possess the same period as the bipolarsinusoidal voltage. Alternatively, the unipolar oscillating voltage maybe formed by passing a DC voltage through a full bridge formed from anyappropriate type of four switching devices.

Embodiments of the present technology may include a method of processinga semiconductor substrate. As shown in FIG. 3, method 300 may includemay include flowing gas through a cavity defined by a powered electrode302. The gas may include argon or helium, and the gas may includefluorinated or perfluorinated compounds. The gas may includesemiconductor processing gases such as NF₃ or NH₃.

The cavity defined by the powered electrode may be conical, cylindrical,substantially conical, or substantially cylindrical. While a planarpowered electrode opposite a planar grounded electrode may result in aconstant distance between the two electrodes, a powered electrode with acavity opposite a planar grounded electrode may provide varyingdistances between the two electrodes. These varying distances may allowfor different diameters and different pD conditions.

Method 300 may further include applying a negative voltage to thepowered electrode 304. The powered electrode may include nickel-coatedaluminum without a dielectric coating. Applying the negative voltage maybe through an electronic ballast. The electronic ballast may be acommercially available electronic ballast. The electronic ballast mayhave a power of between about 50 W and about 100 W, between about 100 Wand about 200 W, between about 75 W and about 125 W, or about 60 W inembodiments. The electronic ballast may have a frequency of less thanabout 1 MHz. The frequency may be less than about 400 kHz, less thanabout 100 kHz, or less than about 60 kHz in embodiments. Too high afrequency may preclude the generation of a hollow cathode, even duringan applied negative voltage. Frequencies less than the plasma frequency,which may be around 1 or 2 MHz, are believed to allow for the generationof the hollow cathode discharge. For example, under certain conditions,a frequency of 13.56 MHz was observed to not result in generation of ahollow cathode discharge during negative swings in voltage.

Also, method 300 may include striking a hollow cathode discharge 306 inthe cavity to form hollow cathode discharge effluents from the gas.Striking the hollow cathode discharge may occur at a pressure betweenabout 1.5 Torr and about 10 Torr, between about 5 Torr and about 10Torr, or between about 1.5 Torr and 5 Torr in embodiments. Pressures mayvary depending on the composition of the gas and the pD condition.

In addition to striking a hollow cathode discharge, method 300 mayinclude flowing the hollow cathode discharge effluents 308 to theprocessing region through a plurality of apertures defined by anelectrically grounded electrode. The electrically grounded electrode mayhave a first surface and a second surface, both of which may besubstantially flat or planar when not considering the apertures. Thefirst surface may be the top surface, and the second surface may be thebottom surface. The grounded electrode may include nickel-coatedaluminum without a dielectric coating. Method 300 may then includereacting the hollow cathode discharge effluents with the semiconductorsubstrate 310 in a processing region. The processing region may beseparate from a plasma region, where the plasma is generated. Theprocessing region and the plasma region may be divided by theelectrically grounded electrode.

Method 300 may further comprise applying a positive voltage to thepowered electrode. Applying the positive voltage may result in strikinga glow discharge to form glow discharge effluents from the gas. Most ofthe glow discharge may be between the powered electrode and theelectrically grounded electrode and not in the cavity. The glowdischarge may be in a position or space different from the position orspace of the hollow cathode. The glow discharge may be positionedfarther away from the powered electrode and closer to the electricallygrounded electrode than the hollow cathode. Method 300 may includestriking a glow discharge without removing the semiconductor substratefrom the processing region. Alternatively, the semiconductor substratemay be removed from the processing region after striking a hollowcathode discharge. Method 300 may include striking a glow discharge witha different semiconductor substrate in the processing region or the samesemiconductor substrate in the processing region after an additionalsemiconductor processing operation. Accordingly, both hollow cathodedischarge processing and glow discharge processing may occur in the sameprocessing region, providing operational flexibility with the processingregion.

As depicted in FIG. 4, embodiments may include a method 400 ofprocessing a semiconductor substrate, where method 400 may includeflowing gas 402 to the processing region. The gas may be any of thegases previously mentioned. Additionally, method 400 may includestriking a hollow cathode discharge 404 to form hollow cathode dischargeeffluents from the gas. The hollow cathode discharge may be located in afirst space in a conical cavity defined by a powered electrode. Strikingthe hollow cathode discharge may include applying a negative voltage tothe powered electrode. Furthermore, method 400 may include reactinghollow cathode discharge effluents with the semiconductor substrate 406in a processing region.

Method 400 may also include striking a glow discharge 408 to form glowdischarge effluents from the gas. The glow discharge may be located in asecond space between the powered electrode and an electrically groundedelectrode. Striking the glow discharge may include applying a positivevoltage to the powered electrode. The second space may be different fromthe first space. The second space may be located farther away from thepowered electrode than the first space, and the second space may beshaped differently than the first space. The second space may be flatterin shape than the first space, while the shape of the first space may bedefined more by the shape of the cavity than the second space. Method400 may further include reacting glow discharge effluents with thesemiconductor substrate 410 in the processing region.

Reacting both hollow cathode discharge effluents and glow dischargeeffluents with the same semiconductor substrate may enable bettercontrol of etching or deposition with more flexibility in tailoring ion,radical, electron, and other densities. Possibly as a result of thehigher densities, higher pressures, or higher intensities, thecomposition of the hollow cathode discharge effluents may be differentfrom the composition of glow discharge effluents. The hollow cathodedischarge effluents may have a higher concentration of radicals thanglow discharge effluents. In addition, the hollow cathode dischargeeffluents may contain different radicals in different proportions thanin glow discharge effluents. These different concentrations andproportions may result in different reactions with the semiconductorsubstrate. Alternating between a hollow cathode discharge and a glowdischarge may allow for better control of reaction chemistries over justa single discharge mode. Better control of reaction chemistries mayresult in higher selectivities or etch rates.

As shown in FIG. 5, embodiments of the present technology may include asystem 500 for processing a semiconductor substrate. System 500 mayinclude a powered electrode 502 electrically coupled with an electronicballast. Additionally, system 500 may include a conical cavity 504defined by powered electrode 502, where conical cavity 504 ischaracterized by a narrower diameter end 506 and a wider diameter end508. The height of conical cavity 504 may be between about 5 cm andabout 20 cm, between about 5 cm and about 10 cm, or between about 10 cmand about 20 cm in embodiments. The narrower diameter may be betweenabout 0 cm and about 1 cm, between about 0 cm and about 0.5 cm, orbetween about 0.5 cm and about 1 cm in embodiments. The wider diametermay be between about 4 cm and about 10 cm, between about 4 cm and about5 cm, or between about 5 cm and about 10 cm in embodiments.

System 500 may further include a power supply 510 electrically coupledwith the electronic ballast, where power supply 510 is configured todeliver a negative voltage to powered electrode 502 to strike a hollowcathode discharge in conical cavity 504. The frequency of the voltagemay be any of the frequencies previously described. System 500 may alsoinclude a gas inlet 512 connected to narrower diameter end 506 of theconical cavity 504.

Furthermore, system 500 may include an electrically grounded electrode514 defining a plurality of apertures, where electrically groundedelectrode 514 is disposed closer to wider diameter end 508 than narrowerend 506 of conical cavity 504. The diameter of an aperture 526 may bebetween about 0.05 cm and about 0.10 cm, between about 0.05 cm and about0.08 cm, or between about 0.08 cm and about 0.10 cm in embodiments.Electrically grounded electrode 514 may have a first surface and asecond surface. The first and second surfaces may be substantially flat,or portions of the first and second surfaces exposed to gas and/orplasma may be substantially flat in embodiments. The first surface maybe parallel to the second surface. Either or both of powered electrode502 and electrically grounded electrode 514 may include a nickel-coatedaluminum without a dielectric coating. Powered electrode 502 andelectrically grounded electrode 514 may be separated by a dielectric516.

System 500 may further include a high-speed intensified charge-coupleddevice (ICCD) camera 518 aligned to record time-resolved images of thehollow cathode discharge and a glow discharge. The time-resolved imagesmay be taken through a viewport 520, which may be near the bottom ofsystem 500. ICCD camera 518 may be aligned so that the camera can detectphotons through the plurality of apertures in electrically groundedelectrode 514. For instance, a path of a photon from a plasma 522 may beillustrated by dashed arrow 524. Photons may pass from cavity 504through an aperture 526 in electrically grounded electrode 514 andthrough a process chamber 528. A semiconductor substrate may be placedin process chamber 528.

ICCD camera 518 may be in communication with an oscilloscope 530. Theoscilloscope may read voltage and current from power supply 510. Acontrol PC or computer 532 may be connected to ICCD camera 518 and/oroscilloscope 530. Images on ICCD camera 518 may then be recorded alongwith voltage/current information at that same time on oscilloscope 530.

Effluents from plasma 522 may also go through aperture 526 and processchamber 528 before going to an outlet 534 leading to a pump. System 500may operate at any of the pressures and voltages previously described.Flowrates may vary from about 500 sccm to about 10 slm.

Exemplary Processing System

Processing chambers that may implement embodiments of the presentinvention may be included within processing platforms such as theCENTURA® and PRODUCER® systems, available from Applied Materials, Inc.of Santa Clara, Calif.

FIG. 6 is a substrate processing chamber 1001 according to embodiments.A remote plasma system 1010 may process a fluorine-containing precursorwhich then travels through a gas inlet assembly 1011. Two distinct gassupply channels are visible within the gas inlet assembly 1011. A firstchannel 1012 carries a gas that passes through the remote plasma system1010 (RPS), while a second channel 1013 bypasses the remote plasmasystem 1010. Either channel may be used for the fluorine-containingprecursor in embodiments. On the other hand, the first channel 1012 maybe used for the process gas and the second channel 1013 may be used fora treatment gas. The lid (or conductive top portion) 1021 and aperforated partition 1053 are shown with an insulating ring 1024 inbetween, which allows a unipolar oscillating voltage to be applied tothe lid 1021 relative to perforated partition 1053. Perforated partition1053 may be an electrically grounded electrode. The unipolar oscillatingvoltage strikes a plasma in chamber plasma region 1020. The process gasmay travel through first channel 1012 into chamber plasma region 1020and may be excited by a plasma in chamber plasma region 1020 alone or incombination with remote plasma system 1010. If the process gas (thefluorine-containing precursor) flows through second channel 1013, thenonly the chamber plasma region 1020 is used for excitation. Thecombination of chamber plasma region 1020 and/or remote plasma system1010 may be referred to as a remote plasma region herein. The perforatedpartition (also referred to as a showerhead) 1053 separates chamberplasma region 1020 from a substrate processing region 1070 beneathshowerhead 1053. Showerhead 1053 allows a plasma present in chamberplasma region 1020 to avoid directly exciting gases in substrateprocessing region 1070, while still allowing excited species to travelfrom chamber plasma region 1020 into substrate processing region 1070.

Showerhead 1053 is positioned between chamber plasma region 1020 andsubstrate processing region 1070 and allows plasma effluents (excitedderivatives of precursors or other gases) created within remote plasmasystem 1010 and/or chamber plasma region 1020 to pass through aplurality of through-holes or apertures 1056 that traverse the thicknessof the plate. The showerhead 1053 also has one or more hollow volumes1051 which can be filled with a precursor in the form of a vapor or gas(such as the fluorine-containing precursor) and pass through blind-holes1055 into substrate processing region 1070 but not directly into chamberplasma region 1020. Showerhead 1053 is thicker than the length of thesmallest diameter 1050 of the through-holes 1056 in embodiments. Tomaintain a significant concentration of excited species penetrating fromchamber plasma region 1020 to substrate processing region 1070, thelength 1026 of the smallest diameter 1050 of the through-holes may berestricted by forming larger diameter portions of through-holes 1056part way through the showerhead 1053. The length of the smallestdiameter 1050 of the through-holes 1056 may be the same order ofmagnitude as the smallest diameter of the through-holes 1056 or less inembodiments. Showerhead 1053 may be referred to as a dual-channelshowerhead, a dual-zone showerhead, a multi-channel showerhead or amulti-zone showerhead to convey the existence of through-holes andblind-holes for introducing precursors.

Showerhead 1053 may be configured to serve the purpose of an ionsuppressor as shown in FIG. 6. Alternatively, a separate processingchamber element may be included (not shown) which suppresses the ionconcentration traveling into substrate processing region 1070. Lid 1021and showerhead 1053 may function as a first electrode and secondelectrode, respectively, so that lid 1021 and showerhead 1053 mayreceive different electric voltages. In these configurations, unipolaroscillating electrical power may be applied to lid 1021, showerhead1053, or both. For example, electrical power may be applied to lid 1021while showerhead 1053 (and/or an ion suppressor) is grounded. Thesubstrate processing system may include a unipolar oscillating voltagegenerator that provides electrical power to the lid 1021 or showerhead1053 while the other is grounded. The voltage applied to lid 1021 mayfacilitate a uniform distribution of plasma (i.e., reduce localizedplasma) within chamber plasma region 1020. To enable the formation of aplasma in chamber plasma region 1020, insulating ring 1024 mayelectrically insulate lid 1021 from showerhead 1053. Insulating ring1024 may be made from a ceramic and may have a high breakdown voltage toavoid sparking Portions of substrate processing chamber 1001 near thecapacitively-coupled plasma components just described may furtherinclude a cooling unit (not shown) that includes one or more coolingfluid channels to cool surfaces exposed to the plasma with a circulatingcoolant (e.g., water).

In the embodiment shown, showerhead 1053 may distribute (viathrough-holes 1056) process gases which contain fluorine, hydrogen,and/or plasma effluents of such process gases upon excitation by aplasma in chamber plasma region 1020. In embodiments, the process gasintroduced into the remote plasma system 1010 and/or chamber plasmaregion 1020 may contain fluorine. The process gas may also include acarrier gas such as helium, argon, nitrogen (N₂), etc. Plasma effluentsmay include ionized or neutral derivatives of the process gas and mayalso be referred to herein as radical-fluorine referring to the atomicconstituent of the process gas introduced.

Through-holes 1056 are configured to suppress the migration ofionically-charged species out of the chamber plasma region 1020 whileallowing uncharged neutral or radical species to pass through showerhead1053 into substrate processing region 1070. These uncharged species mayinclude highly reactive species that are transported with less-reactivecarrier gas by through-holes 1056. As noted above, the migration ofionic species by through-holes 1056 may be reduced, and in someinstances completely suppressed. Controlling the amount of ionic speciespassing through showerhead 1053 provides increased control over the gasmixture brought into contact with the underlying wafer substrate, whichin turn increases control of the deposition and/or etch characteristicsof the gas mixture. For example, adjustments in the ion concentration ofthe gas mixture can alter the etch selectivity (e.g., thesilicon:silicon nitride etch rate ratio).

In embodiments, the number of through-holes 1056 may be between about 60and about 2000. Through-holes 1056 may have a variety of shapes but aremost easily made round. The smallest diameter 1050 of through-holes 1056may be between about 0.5 mm and about 20 mm or between about 1 mm andabout 6 mm in embodiments. There is also latitude in choosing thecross-sectional shape of through-holes, which may be made conical,cylindrical or combinations of the two shapes. The number of blind-holes1055 used to introduce unexcited precursors into substrate processingregion 1070 may be between about 100 and about 5000 or between about 500and about 2000 in different embodiments. The diameter of the blind-holes1055 may be between about 0.1 mm and about 2 mm.

Through-holes 1056 may be configured to control the passage of theplasma-activated gas (i.e., the ionic, radical, and/or neutral species)through showerhead 1053. For example, the aspect ratio of the holes(i.e., the hole diameter to length) and/or the geometry of the holes maybe controlled so that the flow of ionically-charged species in theactivated gas passing through showerhead 1053 is reduced. Through-holes1056 in showerhead 1053 may include a tapered portion that faces chamberplasma region 1020, and a cylindrical portion that faces substrateprocessing region 1070. The cylindrical portion may be proportioned anddimensioned to control the flow of ionic species passing into substrateprocessing region 1070. An adjustable electrical bias may also beapplied to showerhead 1053 as an additional means to control the flow ofionic species through showerhead 1053.

Alternatively, through-holes 1056 may have a smaller inner diameter (ID)toward the top surface of showerhead 1053 and a larger ID toward thebottom surface. In addition, the bottom edge of through-holes 1056 maybe chamfered to help evenly distribute the plasma effluents in substrateprocessing region 1070 as the plasma effluents exit the showerhead andpromote even distribution of the plasma effluents and precursor gases.The smaller ID may be placed at a variety of locations alongthrough-holes 1056 and still allow showerhead 1053 to reduce the iondensity within substrate processing region 1070. The reduction in iondensity results from an increase in the number of collisions with wallsprior to entry into substrate processing region 1070. Each collisionincreases the probability that an ion is neutralized by the acquisitionor loss of an electron from the wall. Generally speaking, the smaller IDof through-holes 1056 may be between about 0.2 mm and about 20 mm. Inother embodiments, the smaller ID may be between about 1 mm and 6 mm orbetween about 0.2 mm and about 5 mm. Further, aspect ratios of thethrough-holes 1056 (i.e., the smaller ID to hole length) may beapproximately 1 to 20. The smaller ID of the through-holes may be theminimum ID found along the length of the through-holes. Thecross-sectional shape of through-holes 1056 may be generallycylindrical, conical, or any combination thereof.

FIG. 7 is a bottom view of a showerhead 1053 for use with a processingchamber according to embodiments. Showerhead 1053 corresponds with theshowerhead shown in FIG. 6. Through-holes 1056 are depicted with alarger inner-diameter (ID) on the bottom of showerhead 1053 and asmaller ID at the top. Blind-holes 1055 are distributed substantiallyevenly over the surface of the showerhead, even amongst thethrough-holes 1056 which helps to provide more even mixing than otherembodiments described herein.

An exemplary patterned substrate may be supported by a pedestal (notshown) within substrate processing region 1070 when fluorine-containingplasma effluents arrive through through-holes 1056 in showerhead 1053.Though substrate processing region 1070 may be equipped to support aplasma for other processes such as curing, no plasma is present duringthe etching of patterned substrate, in embodiments.

A plasma may be ignited either in chamber plasma region 1020 aboveshowerhead 1053 or substrate processing region 1070 below showerhead1053. A plasma is present in chamber plasma region 1020 to produce theradical-fluorine from an inflow of the fluorine-containing precursor. Aunipolar oscillating voltage (shifted or otherwise transformed togenerally confine to one polarity) is applied between the conductive topportion (lid 1021) of the processing chamber and showerhead 1053 toignite a plasma in chamber plasma region 1020 during deposition. Theunipolar oscillating voltage applied to lid 1021 is shifted such to notcenter about the potential of showerhead 1053. A unipolar oscillatingvoltage power supply generates a unipolar oscillating frequency of lessthan or about 1,000 kHz, less than or about 500 kHz, less than or about300 kHz or between 1 kHz and 200 kHz according to embodiments.

The top plasma may be left at low or no power when the bottom plasma inthe substrate processing region 1070 is turned on to either cure a filmor clean the interior surfaces bordering substrate processing region1070. A plasma in substrate processing region 1070 is ignited byapplying the unipolar oscillating voltage between showerhead 1053 andthe pedestal or bottom of the chamber. A cleaning gas may be introducedinto substrate processing region 1070 while the plasma is present.

The pedestal may have a heat exchange channel through which a heatexchange fluid flows to control the temperature of the substrate. Thisconfiguration allows the substrate temperature to be cooled or heated tomaintain relatively low temperatures (from room temperature throughabout 120° C.). The heat exchange fluid may comprise ethylene glycol andwater. The wafer support platter of the pedestal (aluminum, ceramic, ora combination thereof) may also be resistively heated to achieverelatively high temperatures (from about 120° C. through about 1100° C.)using an embedded single-loop embedded heater element configured to maketwo full turns in the form of parallel concentric circles. An outerportion of the heater element may run adjacent to a perimeter of thesupport platter, while an inner portion runs on the path of a concentriccircle having a smaller radius. The wiring to the heater element passesthrough the stem of the pedestal.

The chamber plasma region and/or a region in a remote plasma system maybe referred to as a remote plasma region. In embodiments, the radicalprecursors (e.g. radical-fluorine) are formed in the remote plasmaregion and travel into the substrate processing region where they mayindividually react with chamber walls or the substrate surface. Plasmapower may essentially be applied only to the remote plasma region, inembodiments, to ensure that the radical-fluorine (which may also bereferred to as plasma effluents) are not further excited in thesubstrate processing region.

In embodiments employing a chamber plasma region, the excited plasmaeffluents are generated in a section of the substrate processing regionpartitioned from a deposition region. The deposition region, also knownherein as the substrate processing region, is where the plasma effluentsmix and react to etch the patterned substrate (e.g., a semiconductorwafer). The excited plasma effluents may also be accompanied by inertgases (in the exemplary case, argon). The substrate processing regionmay be described herein as “plasma-free” during etching of thesubstrate. “Plasma-free” does not necessarily mean the region is devoidof plasma. A relatively low concentration of ionized species and freeelectrons created within the remote plasma region do travel throughpores (apertures) in the partition (showerhead/ion suppressor) due tothe shapes and sizes of through-holes 1056. In some embodiments, thereis essentially no concentration of ionized species and free electronswithin the substrate processing region. In embodiments, the electrontemperature may be less than 0.5 eV, less than 0.45 eV, less than 0.4eV, or less than 0.35 eV in substrate processing region 1070 duringexcitation of a remote plasma. The borders of the plasma in the chamberplasma region are hard to define and may encroach upon the substrateprocessing region through the apertures in the showerhead. In the caseof an inductively-coupled plasma, a small amount of ionization may beeffected within the substrate processing region directly. Furthermore, alow intensity plasma may be created in the substrate processing regionwithout eliminating desirable features of the forming film. All causesfor a plasma having much lower intensity ion density than the chamberplasma region (or a remote plasma region, for that matter) during thecreation of the excited plasma effluents do not deviate from the scopeof “plasma-free” as used herein.

The fluorine-containing precursor) may be flowed into chamber plasmaregion 1020 at rates between about 5 sccm and about 500 sccm, betweenabout 10 sccm and about 300 sccm, between about 25 sccm and about 200sccm, between about 50 sccm and about 150 sccm or between about 75 sccmand about 125 sccm in embodiments.

The flow rate of the fluorine-containing precursor into the chamber mayaccount for 0.05% to about 20% by volume of the overall gas mixture; theremainder being carrier gases. The fluorine-containing precursor areflowed into the remote plasma region but the plasma effluents have thesame volumetric flow ratio, in embodiments. A purge or carrier gas maybe initiated into the remote plasma region before that of thefluorine-containing gas to stabilize the pressure within the remoteplasma region.

Plasma power applied to the remote plasma region can be a variety offrequencies or a combination of multiple frequencies. In the exemplaryprocessing system the plasma is provided by unipolar oscillating powerdelivered between lid 1021 and showerhead 1053. The energy is appliedusing a capacitively-coupled plasma unit. The remote plasma source powermay be between about 10 watts and about 3000 watts, between about 20watts and about 2000 watts, between about 30 watts and about 1000 watts,or between about 40 watts and about 500 watts in embodiments.

Substrate processing region 1070 can be maintained at a variety ofpressures during the flow of carrier gases and plasma effluents intosubstrate processing region 1070. The pressure within the substrateprocessing region is below or about 50 Torr, below or about 30 Torr orbelow or about 20 Torr. The pressure may be above or about 0.1 Torr,above or about 0.2 Torr, above or about 0.5 Torr or above or about 1Torr in embodiments. Lower limits on the pressure may be combined withupper limits on the pressure to obtain embodiments.

In one or more embodiments, the substrate processing chamber 1001 can beintegrated into a variety of multi-processing platforms, including theProducer™ GT, Centura™ AP and Endura™ platforms available from AppliedMaterials, Inc. located in Santa Clara, Calif. Such a processingplatform is capable of performing several processing operations withoutbreaking vacuum. Processing chambers that may implement embodiments ofthe present invention may include dielectric etch chambers or a varietyof chemical vapor deposition chambers, among other types of chambers.

Embodiments of the etching systems may be incorporated into largerfabrication systems for producing integrated circuit chips. FIG. 8 showsone such system 1101 of etching, deposition, baking and curing chambersaccording to embodiments. In the figure, a pair of FOUPs (front openingunified pods) 1102 supply substrate substrates (e.g., 300 mm diameterwafers) that are received by robotic arms 1104 and placed into a lowpressure holding areas 1106 before being placed into one of the waferprocessing chambers 1108 a-f. A second robotic arm 1110 may be used totransport the substrate wafers from the low pressure holding areas 1106to the wafer processing chambers 1108 a-f and back. Each waferprocessing chamber 1108 a-f, can be outfitted to perform a number ofsubstrate processing operations including the dry etch processesdescribed herein in addition to cyclical layer deposition (CLD), atomiclayer deposition (ALD), chemical vapor deposition (CVD), physical vapordeposition (PVD), etch, pre-clean, degas, orientation and othersubstrate processes.

The wafer processing chambers 1108 a-f may include one or more systemcomponents for depositing, annealing, curing and/or etching a dielectricfilm on the substrate wafer. In one configuration, two pairs of theprocessing chamber (e.g., 1108 c-d and 1108 e-f) may be used to depositdielectric material on the substrate, and the third pair of processingchambers (e.g., 1108 a-b) may be used to etch the deposited dielectric.In another configuration, all three pairs of chambers (e.g., 1108 a-f)may be configured to etch a dielectric film on the substrate. Any one ormore of the processes described may be carried out on chamber(s)separated from the fabrication system shown in different embodiments.

The substrate processing system is controlled by a system controller. Inan exemplary embodiment, the system controller includes a hard diskdrive, and a processor. The processor contains a single-board computer(SBC), analog and digital input/output boards, interface boards andstepper motor controller boards. Various parts of CVD system conform tothe Versa Modular European (VME) standard which defines board, cardcage, and connector dimensions and types. The VME standard also definesthe bus structure as having a 16-bit data bus and a 24-bit address bus.

System controller 1157 is used to control motors, valves, flowcontrollers, power supplies and other functions required to carry outprocess recipes described herein. A gas handling system 1155 may also becontrolled by system controller 1157 to introduce gases to one or all ofthe wafer processing chambers 1108 a-f. System controller 1157 may relyon feedback from optical sensors to determine and adjust the position ofmovable mechanical assemblies in gas handling system 1155 and/or inwafer processing chambers 1108 a-f. Mechanical assemblies may includethe robot, throttle valves and susceptors which are moved by motorsunder the control of system controller 1157.

In an exemplary embodiment, system controller 1157 includes a hard diskdrive (memory), USB ports, and a processor. System controller 1157includes analog and digital input/output boards, interface boards andstepper motor controller boards. Various parts of multi-chamberprocessing system 1101 which contains substrate processing chamber 1001are controlled by system controller 1157. The system controller executessystem control software in the form of a computer program stored oncomputer-readable medium such as a hard disk, a floppy disk, a flashmemory thumb drive, or a network drive. Other types of memory can alsobe used. The computer program includes sets of instructions that dictatethe timing, mixture of gases, chamber pressure, chamber temperature, RFpower levels, susceptor position, and other parameters of a particularprocess.

A process for etching, depositing or otherwise processing a film on asubstrate or a process for cleaning chamber can be implemented using acomputer program product that is executed by the controller. Thecomputer program code can be written in any conventional computerreadable programming language: for example, 68000 assembly language, C,C++, Pascal, Fortran, or others. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor, andstored or embodied in a computer usable medium, such as a memory systemof the computer. If the entered code text is in a high level language,the code is compiled, and the resultant compiler code is then linkedwith an object code of precompiled Microsoft Windows® library routines.To execute the linked, compiled object code the system user invokes theobject code, causing the computer system to load the code in memory. TheCPU then reads and executes the code to perform the tasks identified inthe program.

The interface between a user and the controller may be via atouch-sensitive monitor and may also include a mouse and keyboard. Inone embodiment two monitors are used, one mounted in the clean room wallfor the operators and the other behind the wall for the servicetechnicians. The two monitors may simultaneously display the sameinformation, in which case only one is configured to accept input at atime. To select a particular screen or function, the operator touches adesignated area on the display screen with a finger or the mouse. Thetouched area changes its highlighted color, or a new menu or screen isdisplayed, confirming the operator's selection.

Example 1

In this example, plasmas were generated in a system, where the totalheight of conical cavity defined by powered electrode is 10 cm. Thediameter at the top of cavity was 0.5 cm, and the diameter at the bottomof cavity was 5 cm. Apertures in electrically grounded electrode have adiameter of 0.08 cm. Both the powered electrode and the electricallygrounded electrode were made of nickel-coated aluminum without anydielectric coating. The setup was a direct-current type resistive plasmadevice, without a phase difference between voltage and current.

A commercial electronic ballast with a maximum power of 100 W was usedto generate a plasma. The commercial electronic ballast in this examplewas an electronic ballast for household fluorescent lamps. Theelectronic ballast had an output frequency of 60 to 100 kHz and a 0 to10 V control for dimming. The voltage was measured with a 100:1 voltageprobe (PPE2 KV, LeCroy®), and the current was measured with a currentprobe (P6021, Textronix®). The voltage-current (V-I) waveforms wererecorded to an oscilloscope (WaveRunner® 640zi, LeCroy®). Time-resolveddischarge images were measure with a high-speed intensifiedcharge-coupled device (ICCD), Andor®).

Argon was introduced from the top of the powered electrode. The flow ofargon was controlled by a mass flow controller. Argon at 500 sccmmaintained the pressure at 1.5 Torr. Increasing the argon flowrate to 8slm increased the pressure to 27 Torr.

Example 2

From the system setup in Example 1, the peak voltages were 707 V and−290 V, as shown in FIG. 9(a). The positive and negative peak currentswere 270 mA and −398 mA, respectively, as shown in FIG. 9(b). Thevoltage waveform was biased around 200 V. Pressure was varied between1.5 Torr and 27 Torr. The voltage bias decreased with increasingpressure. In the positive half cycle, as the pressure increased, thevoltage decreased and the current increased.

At 1.5 Torr, in the positive half cycle of the period with the poweredelectrode being an anode, the peak current was about 30 percent lowerthan that in the negative half cycle when the powered electrode was acathode, even though the actual applied voltage was about 2.4 timeshigher. The total charge transferred during positive and negative cycleswere 1.69 C and 1.65 C, respectively, which was only different by about2.5%. The results imply that the discharge phenomena of the positive andnegative half cycles may be different.

As shown in FIG. 9(a), when pressure increased to 8.8 Torr, peak voltagein the positive half cycle decreased. The magnitude of the peak voltagein the positive half cycle was about equal to the magnitude of the peakvoltage in the negative half cycle. With current, as shown in FIG. 9(b),when pressure increases to 8.8 Torr, peak current in the positive halfcycle increased. The magnitude of the peak current in the positive halfcycle was about equal to the magnitude of the peak current in thenegative half cycle. Both the current and voltage swings in the positiveand negative cycles became more similar and balanced at this increasedpressure. And at this increased pressure, the intensities of the glowdischarge and hollow cathode discharge became similar. This exampleshows that varying the pressure may affect the characteristics of eachdischarge mode.

Example 3

Time-resolved images from discharges generated in the system in Example2 are shown in FIG. 10. The exposure time for these images was 0.5 μs.The images from the glow discharge appear different than the images fromthe hollow cathode discharge. The hollow cathode discharge images wereobserved to be more intense than the glow discharge images.

At 8.8 Torr, the glow discharge images show strong emissions in the teno'clock direction of the grounded electrode. This observation, alongwith the electrical characteristics at this pressure in Example 2,suggests that a hollow cathode discharge may be present at a pressure of8.8 Torr with a pD of about 0.7 Torr-cm (D=0.08 cm). As can be seen inthe image, this discharge is not uniform, and may not be desirable forsemiconductor processing.

The hollow cathode discharge mode in the negative half cycle wassustained up to 8.8 Torr and became more intense with increasingpressure. Because the diameter of the intense light emission from thehollow cathode discharge is about 2 cm, pD for stable operation of thismode should be about 3 to 20 Torr-cm for the electrode configuration inExample 1. Stable operation of the glow discharge mode would be atpressures at less than 2.4 Torr, with the glow discharge at 4.1 Torrshowing some non-uniformities. As the pressure was increased to 27 Torr(not shown in FIG. 10), discharges in both the positive half cycle andthe negative half cycle became unstable and started to extinguish.

As used herein “substrate” may be a support substrate with or withoutlayers formed thereon. The patterned substrate may be an insulator or asemiconductor of a variety of doping concentrations and profiles andmay, for example, be a semiconductor substrate of the type used in themanufacture of integrated circuits. Exposed “silicon” of the patternedsubstrate is predominantly Si but may include minority concentrations ofother elemental constituents (e.g. nitrogen, oxygen, hydrogen, carbon).Exposed “silicon nitride” of the patterned substrate is predominantlySi₃N₄ but may include minority concentrations of other elementalconstituents (e.g. oxygen, hydrogen, carbon). Exposed “silicon oxide” ofthe patterned substrate is predominantly SiO₂ but may include minorityconcentrations of other elemental constituents (e.g. nitrogen, hydrogen,carbon). In some embodiments, silicon oxide films etched using themethods disclosed herein consist essentially of silicon and oxygen.

The term “precursor” is used to refer to any process gas which takespart in a reaction to either remove material from or deposit materialonto a surface. “Plasma effluents” describe gas exiting from the chamberplasma region and entering the substrate processing region. Plasmaeffluents are in an “excited state” wherein at least some of the gasmolecules are in vibrationally-excited, dissociated and/or ionizedstates. A “radical precursor” is used to describe plasma effluents (agas in an excited state which is exiting a plasma) which participate ina reaction to either remove material from or deposit material on asurface. “Radical-fluorine” is a radical precursor that containsfluorine but may contain other elemental constituents. The phrase “inertgas” refers to any gas which does not form chemical bonds when etchingor being incorporated into a film. Exemplary inert gases include noblegases but may include other gases so long as no chemical bonds areformed when (typically) trace amounts are trapped in a film.

The terms “gap” and “trench” are used throughout with no implicationthat the etched geometry has a large horizontal aspect ratio. Viewedfrom above the surface, trenches may appear circular, oval, polygonal,rectangular, or a variety of other shapes. A trench may be in the shapeof a moat around an island of material. The term “via” is used to referto a low aspect ratio trench (as viewed from above) which may or may notbe filled with metal to form a vertical electrical connection. As usedherein, a conformal etch process refers to a generally uniform removalof material on a surface in the same shape as the surface, i.e., thesurface of the etched layer and the pre-etch surface are generallyparallel. A person having ordinary skill in the art will recognize thatthe etched interface likely cannot be 100% conformal and thus the term“generally” allows for acceptable tolerances.

In the preceding description, for the purposes of explanation, numerousdetails have been set forth in order to provide an understanding ofvarious embodiments of the present technology. It will be apparent toone skilled in the art, however, that certain embodiments may bepracticed without some of these details, or with additional details.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theembodiments. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent technology. Accordingly, the above description should not betaken as limiting the scope of the technology.

Where a range of values is provided, it is understood that eachintervening value, to the smallest fraction of the unit of the lowerlimit, unless the context clearly dictates otherwise, between the upperand lower limits of that range is also specifically disclosed. Anynarrower range between any stated values or unstated intervening valuesin a stated range and any other stated or intervening value in thatstated range is encompassed. The upper and lower limits of those smallerranges may independently be included or excluded in the range, and eachrange where either, neither, or both limits are included in the smallerranges is also encompassed within the technology, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either or both ofthose included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural references unless the context clearly dictatesotherwise. Thus, for example, reference to “an aperture” includes aplurality of such apertures, and reference to “the gas” includesreference to one or more gases and equivalents thereof known to thoseskilled in the art, and so forth.

Also, the words “comprise(s)”, “comprising”, “contain(s)”, “containing”,“include(s)”, and “including”, when used in this specification and inthe following claims, are intended to specify the presence of statedfeatures, integers, components, or operations, but they do not precludethe presence or addition of one or more other features, integers,components, operations, acts, or groups.

The invention claimed is:
 1. A method of processing a semiconductorsubstrate, the method comprising: flowing a gas through a cavity definedby a powered electrode; applying a negative voltage to the poweredelectrode; striking a hollow cathode discharge in the cavity to formhollow cathode discharge effluents from the gas; flowing the hollowcathode discharge effluents to a processing region through a pluralityof apertures defined by an electrically grounded electrode; and reactingthe hollow cathode discharge effluents with the semiconductor substratein the processing region, wherein: applying the negative voltagecomprises applying the negative voltage through an electronic ballast,and the electronic ballast has a frequency of less than about 1 MHz. 2.The method of claim 1, wherein the method further comprises: applying apositive voltage to the powered electrode; striking a glow discharge toform glow discharge effluents from the gas, wherein most of the glowdischarge is between the powered electrode and the electrically groundedelectrode and not in the cavity; flowing glow discharge effluents to theprocessing region through the plurality of apertures; and reacting theglow discharge effluents with the semiconductor substrate in theprocessing region.
 3. The method of claim 1, wherein the gas comprisesargon or helium.
 4. The method of claim 3, wherein the gas furthercomprises fluorinated compounds.
 5. The method of claim 1, wherein thegas comprises NF₃ or NH₃.
 6. The method of claim 4, wherein the cavityis conical.
 7. The method of claim 6, wherein the electrically groundedelectrode has a first surface and a second surface, and the firstsurface and the second surface are substantially flat.
 8. The method ofclaim 1, wherein the cavity is cylindrical.
 9. The method of claim 7,wherein striking the hollow cathode discharge comprises striking thehollow cathode discharge at a pressure between about 1.5 Torr and about10 Torr.
 10. The method of claim 9, wherein the powered electrodecomprises nickel-coated aluminum without a dielectric coating and theelectrically grounded electrode comprises nickel-coated aluminum withouta dielectric coating.
 11. The method of claim 10, wherein the electronicballast has a power of about 60 W.
 12. A method of processing asemiconductor substrate, the method comprising: flowing a gas to aprocessing region; striking a hollow cathode discharge to form hollowcathode discharge effluents from the gas; reacting hollow cathodedischarge effluents with the semiconductor substrate in the processingregion; striking a glow discharge to form glow discharge effluents fromthe gas; and reacting the glow discharge effluents with thesemiconductor substrate in the processing region, wherein: striking thehollow cathode discharge comprises applying a negative voltage to apowered electrode through an electronic ballast, and the electronicballast has a frequency of less than about 1 MHz.
 13. The method ofclaim 12, wherein striking the hollow cathode discharge comprisesstriking the hollow cathode discharge in a first space in a conicalcavity defined by the powered electrode.
 14. The method of claim 13,wherein striking the glow discharge comprises striking the glowdischarge in a second space between the powered electrode and anelectrically grounded electrode, wherein the second space is differentfrom the first space.
 15. The method of claim 12, wherein striking theglow discharge further comprises applying a positive voltage to thepowered electrode.
 16. A system for processing a semiconductorsubstrate, the system comprising: a powered electrode electricallycoupled with an electronic ballast; a conical cavity defined by thepowered electrode, wherein the conical cavity is characterized by anarrower diameter end and a wider diameter end; a power supplyelectrically coupled with the electronic ballast, wherein the powersupply is configured to deliver a negative voltage at a frequency belowabout 1 MHz to the powered electrode to strike a hollow cathodedischarge in the conical cavity; a gas inlet connected to the narrowerdiameter end of the conical cavity; and an electrically groundedelectrode defining a plurality of apertures, wherein: the electricallygrounded electrode is disposed closer to the wider diameter end of theconical cavity than the narrower diameter end of the conical cavity, theelectrically grounded electrode has a first surface and a secondsurface, the first surface and the second surface are substantiallyflat, and the first surface is parallel to the second surface.
 17. Thesystem of claim 16, wherein the system further comprises a high-speedintensified charge-coupled device (ICCD) aligned to record time-resolvedimages of the hollow cathode discharge and a glow discharge.
 18. Thesystem of claim 16, wherein the powered electrode comprisesnickel-coated aluminum without a dielectric coating and the electricallygrounded electrode comprises nickel-coated aluminum without a dielectriccoating.
 19. The method of claim 1, wherein the electronic ballast has apower between about 50 W and about 100 W.
 20. The method of claim 2,wherein the negative voltage and the positive voltage are applied assinusoidal oscillating voltages.